Age of Typical FMF Patient Presentation
Familial Mediterranean Fever typically presents in early childhood, with the majority of patients (approximately 60-70%) experiencing their first attack before 5 years of age, though diagnosis is often significantly delayed. 1, 2, 3
Age at Symptom Onset
Most patients develop their first FMF attack during early childhood, with mean age at symptom onset ranging from 1.1 to 13.8 years across different cohorts 4, 3
Approximately 31% of FMF patients present with their first attack at ≤2 years of age, representing a substantial early-onset population 3
About 69% of pediatric FMF patients have symptom onset at ≤5 years of age, 26% between 6-11 years, and only 5% at ≥12 years 2
The disease rarely begins in adulthood, though late-onset cases do occur 5
Delay in Diagnosis
There is a substantial diagnostic delay, with patients experiencing symptoms for years before diagnosis is established 4, 1, 3
Patients with earlier disease onset (≤3 years) experience longer diagnostic delays (mean 3.2 years) compared to those with later onset (mean 1.9 years) 3
In one European cohort, the mean delay to diagnosis was 8.2 years, with mean age at diagnosis of 22.0 years despite symptom onset at 13.8 years 4
Younger patients (diagnosed at ≤2 years) often present atypically with fever alone (40% vs 8.4% in older children), contributing to diagnostic delay 3
Clinical Implications by Age
Younger age at onset (≤5 years) correlates with more severe disease, including higher international severity scoring system (ISSF) scores and more frequent M694V homozygosity 1, 2
Patients with early onset (≤3 years) have significantly higher rates of fever and peritonitis compared to later-onset patients 1
Adolescent patients (≥12 years at onset) have less frequent fever attacks but significantly worse treatment compliance (58.3% vs 90.5% in younger children) 2
Treatment compliance is critical in younger patients who paradoxically show better adherence (90.5% in ≤5 years) despite more severe disease 2
Key Diagnostic Pitfalls
Clinicians must maintain high suspicion in young children with recurrent fever, as atypical presentations (fever without serositis) are common in the first 2 years of life 3
Unnecessary abdominal surgeries are common before diagnosis, with one study reporting 17 of 53 patients (32%) undergoing surgery prior to FMF diagnosis 4
The disease can occur without family history and in non-Mediterranean individuals, so absence of these features should not exclude the diagnosis 5